new generic freertos task interface

osal/FreeRTOS/FixedTimeslotTask.cpp

@@ -157,6 +157,6 @@ ReturnValue_t FixedTimeslotTask::sleepFor(uint32_t ms) {
 	return HasReturnvaluesIF::RETURN_OK;
 }
 
-TaskHandle_t FixedTimeslotTask::getTaskHandle() const {
+TaskHandle_t FixedTimeslotTask::getTaskHandle() {
     return handle;
 }